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common elements between list of lists and lists

 
 
antar2
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      07-17-2008
Hello,

I am a beginner in python.
following program prints the second element in list of lists 4 for the
first elements in list 4 that are common with the elements in list 5


list4 = [['1', 'a'],['4', 'd'],['8', 'g']]
list5 = ['1', '2', '3']

for j in list4:
for k in list5:
if j[0] == k:
print j[1]

Result: a

I would like to do the same thing starting with following lists, where
the numbers in list 5 are without ''. Is there a way to convert
integers in a list to integers in '' ? This is based on a situation
where I want to find common numbers between a list and a list of lists
where the numbers in the list are without '' and the numbers in the
list of lists are with ''


list4 = [['1', 'a'],['4', 'd'],['8', 'g']]
list5 = [1, 2, 3]

This might be a stupid question, but anyway, thanks for your answer
It is not my first post on this site. In some way it is not possible
to react on the messages that I receive to thank the persons that
react. Anyway, thanks a lot


 
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Alexandr N Zamaraev
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      07-17-2008
>>> list4 = [['1', 'a'],['4', 'd'],['8', 'g']]
>>> list5 = [1, 2, 3]
>>> set5 = set(list5)
>>> [x for n, x in list4 if int(n) in set5]

['a']

 
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Bighead
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      07-17-2008
On Jul 17, 4:30 pm, antar2 <(E-Mail Removed)> wrote:
> Hello,
>
> I am a beginner in python.
> following program prints the second element in list of lists 4 for the
> first elements in list 4 that are common with the elements in list 5
>
> list4 = [['1', 'a'],['4', 'd'],['8', 'g']]
> list5 = ['1', '2', '3']
>
> for j in list4:
> for k in list5:
> if j[0] == k:
> print j[1]
>
> Result: a
>
> I would like to do the same thing starting with following lists, where
> the numbers in list 5 are without ''. Is there a way to convert
> integers in a list to integers in '' ? This is based on a situation
> where I want to find common numbers between a list and a list of lists
> where the numbers in the list are without '' and the numbers in the
> list of lists are with ''
>
> list4 = [['1', 'a'],['4', 'd'],['8', 'g']]
> list5 = [1, 2, 3]
>
> This might be a stupid question, but anyway, thanks for your answer
> It is not my first post on this site. In some way it is not possible
> to react on the messages that I receive to thank the persons that
> react. Anyway, thanks a lot


By "integer without ''" you mean integers not embraced by single
quotes, right?

Actually, '1' is a string, not an integer. If you want to normalize
the first elements of all the lists in list4, just use int() to
convert them.

That is:

list4 = [['1', 'a'],['4', 'd'],['8', 'g']]
list5 = ['1', '2', '3']

set5 = set(map(int, list5))
list4 = [[int(i[0]), i[1]] for i in list4]

for j in list4:
if j[0] in set5: print j[1]

You can have a try
 
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